Understanding the Effects Small Scale Heterogeneity on Buoyancy Driven CO2 Migration for Capillary Trapped Storage Capacity Estimation

Abstract

During geologic carbon sequestration, the long term movement and migration of CO2 occurring far from the wells, is majorly controlled by the interplay between buoyancy and capillary forces. Geological heterogeneity, which is well known to affect the fluid flow in the subsurface, becomes an even more pronounced influence in capillary dominated flows. In such cases, core-flooding and numerical experiments have shown that capillary pressure contrasts due to small scale heterogeneities can affect the flow path of the invading CO2 resulting in back filling and accumulation beneath capillary barriers. In this work, we investigate the impact of small-scale heterogeneity on CO2 trapping capacity by simulating the migration of CO2 through nature mimicking high resolution geological domains. Realistic sedimentary 3D models to be used as flow domains are generated for 4 common fluvial clastic facies with accurately represented bedform morphology. The models are populated with petrophysical parameters representative of sandstone lithologies with different grain sizes and sorting. A modified invasion percolation simulator is employed to enable the use of high resolution models and capture the relevant flow physics. Results from these simulations provide insight into how the saturation aka the storage capacity is a non-linear function of the capillary contrast, which suggests some predictive ability is achievable from common sedimentological descriptors.